A semiconductor module is widely used in a power conversion system typically used in a hybrid automobile, an electric automobile, or the like. This kind of semiconductor module configuring a control device for energy saving includes a power semiconductor device which controls large current. A normal power semiconductor device generates heat when controlling large current, but the amount of heat generated by the power semiconductor device increases as the size of the power conversion system is reduced and the output thereof is increased. Therefore, the method of cooling a semiconductor module including a plurality of power semiconductor devices becomes a major problem.
A liquid cooling device has heretofore been used in order to improve the cooling efficiency of a semiconductor module. For the liquid cooling device, various ideas have been made in order to improve the cooling efficiency thereof, such as increasing a refrigerant flow rate, forming radiating fins (a cooling body) in a shape with good heat transfer coefficient, or increasing the heat conductivity of a material forming the tins.
However, when increasing the flow rate of the refrigerant supplied to the cooling device or using a complex fin shape with good heat transfer coefficient, a load on a cooling pump for circulating the refrigerant increases, such as due to an increase in refrigerant pressure loss inside the device. In particular, with a cooling device which cools a large number of power semiconductor devices using a plurality of heat sinks, an increase in pressure loss is noticeable in the case of a flow path configuration wherein a plurality of flow paths is connected in series. In order to reduce the pressure loss, it is ideal to use a configuration which enhances cooling efficiency with a low refrigerant flow rate, and it is only necessary to improve, for example, the heat conductivity of a fin material, but there is an issue that the employment of a fin material having high heat conductivity leads to an overall cost increase of the device.
Heretofore, in order to reduce the pressure loss while maintaining cooling performance, a cooling device has been considered wherein a refrigerant inlet flow path for supplying the refrigerant and a refrigerant outlet flow path for discharging the refrigerant are aligned parallel to each other, and a plurality of heat sinks is disposed between the inlet and outlet flow paths in a direction of refrigerant circulation substantially perpendicular to the flow paths (refer to PTLs 1 to 8). In this case, the refrigerants flow in parallel between the fins configuring the heat sinks, meaning that it is possible to improve cooling performance, and it is possible to reduce the refrigerant pressure loss in the flow paths (refer to PTL 5)
Also, PTL 3 describes a liquid cooling device wherein flow paths (header channels 11a and 11b) which feed in and discharge a cooling liquid are disposed in the same side surface of the module, and each flow path is disposed in a direction perpendicular to fins without changing the sectional area (refer to FIG. 1). Thus, it is possible to minimize a pressure loss incurred in the cooling liquid.
Also, PTL 6 describes a liquid cooling device wherein the whole rear sidewall of a casing forming a cooling liquid inflow portion is smoothly inclined frontward from a right sidewall side toward a left sidewall side, and the flow path sectional area of an entrance header portion decreases from a cooling liquid entrance side toward the left sidewall side. Thus, a flow velocity distribution in the whole flow path of parallel flow path portions of the casing, that is, a flow velocity distribution in a direction of width of the parallel flow path portions, is made uniform.